FIGS. 2 and 3 show a substrate 2 having a silicon structure, a lower oxide 2, a buried conductor path 3 composed of polysilicon, an upper oxide 4, a sensor base 6 composed of epitaxial polysilicon, a bonding pad 7 composed of aluminum, a bonding pad base 8 composed of epitaxial polysilicon having a first region 8a and a second region 8b, a sealing glass 9, a silicon protective cap 10, a contact hole 11, an underetched region 12, dirt particles 13, an oscillator 20, a G-sensor 30 having a comb structure, and a silicon wafer 100.
The micromechanical acceleration sensor constructed in this manner uses this conventional bonding pad structure to pass an electrical connection from, for example, an analog sensor structure provided under silicon protective cap 10, through under sensor base 6 (while guaranteeing hermetic sealing), into the vicinity of the sensor, and to make it bondable there.
As shown in FIG. 3, in the case of the usual bonding pad structure, an underetching of the bonding pad base 8 occurs in region 12 during etching of the first and second oxide layers, which serve at the same time as sacrificial layers for the comb structure of G-sensor 30. Dirt particles 13, such as those formed in particular during sawing in the form of sawing slurry, can become lodged there and can result in electrical short circuits between bonding pad base 8 and substrate 1, or between bonding pad base 8 and conductor path layer 3.
An object of the present invention is to prevent such short circuits in a simple manner.
A first approach toward preventing underetching of the bonding pads provides for covering the trenches around the bonding pads with negative resist during sacrificial oxide etching.
The fact that this is difficult in terms of process technology with step heights of more than approximately 10 .mu.m, and is not even possible with all sensor structures, is a disadvantage of the first above-described approach. In addition, the negative resist must be removed immediately after HF gas-phase etching of the sacrificial layer, since it soaks up HF and can then no longer prevent underetching. In addition, complete removal of the resist in the trenches is complex, and even minor residues can cause the comb structures to stick.